The present invention relates generally to valve operating rocker arms for internal combustion engines and, more particularly, to an improved lightweight rocker arm of the cam follower type.
As a consequence of fuel shortages and concern for the environment, the trend in the automotive industry for many years has been to reduce the fuel consumption of and the generation of pollutants by modern automobiles. To accomplish these goals, the sizes and weights of automobiles have been generally reduced and the engines made more efficient. With higher engine efficiencies, typically due to more accurate control both of fuel input and ignition, engines can also be reduced in size to further contribute to weight reduction. In addition to engine size, the engine components can themselves be reduced in weight with such weight reductions also contributing to engine performance, particularly where components of the movable valve system are affected.
To this end, aluminum alloy rocker arms have been used in the prior art as disclosed, for example, in U.S. Pat. No. 4,147,074 and Japan No. 62-38810. To help ensure light weight, sliding surfaces of the disclosed rocker arms are formed as small inserts of steel alloy or a composite layer where infra-metallic compound particles are scattered in the aluminum alloy matrix, respectively. Cam follower rocker arms are disclosed in U.S. Pat. Nos. 4,614,171 and 4,697,473 wherein machined metal cam rollers are preferably supported for rotation within the rocker arms by needle bearings. The former cam follower rocker arm is formed to ensure proper lubrication of the arm while the later is formed to present a low profile and reduced friction such that, among other benefits, the weight of the rocker arm can be reduced.
While the known structures contribute to the provision of light weight, efficiency and high performance of modern engines, there is a continuing need for improvements in the automotive industry to further enhance engine performance and efficiency, and to further reduce the weight of engines and engine components.